1. Field of the Invention
The present invention relates to a diagnostic table which can be tilted, as well as a medical imaging apparatus including the diagnostic table.
2. Discussion of the Related Art
In a medical imaging apparatus such as, for example, an X-ray diagnosis apparatus, a diagnostic table is used as a part of or independent of the medical imaging apparatus. A patient who to be imaged by the medical imaging apparatus typically lies on a tabletop of the diagnostic table. One known tabletop is usually controlled to change its position so that the patient can be positioned appropriately to be imaged by the medical imaging apparatus. The tabletop may be moved in various directions, for example, upwards and downwards, along its longitudinal direction or a body axis of the patient lying on the tabletop, and/or along a left/right direction of the patient lying on the tabletop (i.e., a lateral direction). The tabletop may also be rotated and/or be tilted. An operator of the diagnostic table typically operates an operation unit of the diagnostic table so that the tabletop may be adjusted to an appropriate position for imaging the patient by a motor provided in the diagnostic table.
When power is supplied to the diagnostic table, a magnetic brake fixes the position of the tabletop. If the operator, for example, grasps a grip of the tabletop when the tabletop is kept horizontally, a switch provided in the grip is activated in response to the grasp. Accordingly, the magnetic brake is released so that the operator can manually move the tabletop horizontally along the longitudinal direction and the lateral direction. Such direction movement is referred to as a floating operation. Further, in response to the release of the magnetic brake, the operator can rotate the tabletop horizontally. Such a rotation is referred to as a panning operation.
A first gear, which can be activated by a gear motor, is also provided in the diagnostic table. The first gear may be formed like a disk and have teeth along an edge of the disk. The diagnostic table further includes the second gear magnetically coupled to the first gear when the second gear is engaged with the first gear. The second gear is formed in a toric shape and has inner teeth along the inside of the toric shape. The first gear can be inserted into the inside of the second gear. The teeth of the first gear are engaged with the inner teeth of the second gear. Such a relationship between the first gear and the second gear may be called a tooth clutch. The second gear also has outer teeth along an edge of the toric shape. The tabletop has teeth on the side opposite to the side where the patient lies. The outer teeth of the second gear may be engaged with the teeth of the tabletop.
In the above configuration, when the operator activates a tabletop tilt button to tilt the tabletop, the first gear is inserted into the inside of the second gear, and the teeth of the first gear are magnetically coupled to and engaged by the teeth of the second gear. Also in response to the activation of the tabletop tilt button, another motor (tilt motor) is activated to tilt the tabletop. During tilting, the tabletop is fixed by the magnetic brake and the tooth clutch operation at a position determined before tilting. When the tilt position is determined, the tilt motor is stopped in response to deactivation of the tabletop tilt button by the operator. If it is necessary to adjust a position of the tabletop along the tilt, that is, for example, along the longitudinal direction of the tabletop, a tabletop longitudinal movement button is activated by the operator. In response to the activation, the gear motor is activated (or rotated) to rotate the first gear while the magnetic brake is released from the tabletop. Since the first gear has been already engaged with the second gear, the tabletop is moved along the longitudinal direction by the second gear, which is rotated by the first gear. Consequently, the patient lying on the tabletop can be positioned appropriately for imaging by the X-ray diagnosis apparatus. After the movement along the longitudinal direction, the magnetic brake is activated again.
After imaging, the tabletop may be tilted back to the horizontal position in a manner similar to the above description, and the engagement of the tooth clutch is released. Also the magnetic brake can be released to allow the floating operation and the panning operation. After the power supply to the diagnostic table is terminated, the magnetic brake may attract the tabletop with its remaining magnetic force.
Examples of the above-described diagnostic table are described in Japanese patent application publication nos. PH07-88102 and UH06-3306.
When the patient is lying on the tabletop, the gross weight of the tabletop and the patient may be approximately one hundred to one hundred and fifty kilograms, or more. Such weight is applied to the magnetic brake and the tooth clutch. When the tabletop is tilted, if a deficiency exists within the tooth clutch and/or the gear motor such that the teeth of the first gear and the inner teeth of the second gear cannot satisfactorily engage with one another, the magnetic brake may not be able to support the weight when the weight is greater than a predetermined maximum weight of the magnetic brake. The deficiency may be, for example, worn-out of the teeth of the first gear, the inner teeth of the second gear, the outer teeth of the second gear, a gear of the gear motor, the gear of the tabletop, and/or reduction gear(s) coupled to the motor if provided. Another possible deficiency may be damage to one or more signal lines to the gear motor, leakage of oil for the reduction gear(s), and/or the like. Also the deficiency may be a breakdown of the gear motor, a breakdown of a reduction unit connected to the gear motor due to oil leakage, a breakdown of internal coils which control the coupling of the gears in the tooth clutch, and/or a break of one or more power lines to the internal coils.
As a result, the tabletop cannot be fixed, and may slide. The tabletop is likely to slide to a greater degree as the tabletop is increasingly tilted.
It is important to prevent or limit this sliding to ensure the safety of the patient. One way to prevent the sliding may be an installation of another tooth clutch. Such a solution, however, complicates the diagnostic table. Further, the tabletop may still slide even after providing another tooth clutch, depending on the weight and a tilted angle. Particularly, when there is deficiency in the gear of the tabletop, the provision of another tooth clutch may not prevent the tabletop from sliding.